Soil development in winter conditions.

IN in construction, of the total volume of earthworks, from 20 to 25% is carried out in winter conditions, while the proportion of soil excavated in a frozen state remains constant - 10-15% with the absolute value of this volume increasing from year to year.

IN In construction practice, there is a need to develop soils that are in a frozen state only in the winter period of the year, i.e. soils with seasonal freezing, or throughout the year, i.e. permafrost soils.

Development of permafrost soils can be carried out using the same methods as seasonally frozen soils. However, when constructing earthen structures in permafrost conditions, it is necessary to take into account specific features geothermal regime of permafrost soils and changes in soil properties when it is disturbed.

At negative temperatures freezing of water contained in the pores of the soil significantly changes the construction and technological properties of non-rocky soils. In frozen soils, the mechanical strength increases significantly, and therefore, their development with earth-moving machines is difficult or even impossible without preparation.

The depth of freezing depends on the air temperature, the duration of exposure to negative temperatures, the type of soil, etc.

Excavation work in winter is carried out using the following three methods. The first method involves preliminary preparation of soils followed by their development using conventional methods; in the second case, frozen soils are pre-cut into blocks; with the third method, soils are developed without them preliminary preparation. Preliminary preparation of soil for development in winter consists of protecting it from freezing, thawing frozen soil, and preliminary loosening of frozen soil.

Protecting the soil from freezing. It is known that availability during the daytime

the surface of the thermal insulation layer reduces both the period and depth of freezing. After withdrawal surface waters You can arrange a thermal insulation layer in one of the following ways.

Loosening the soil. When plowing and harrowing the soil in an area intended for development in winter, its upper layer acquires a loose structure with closed voids filled with air, which has sufficient thermal insulation properties. Plowing is carried out with tractor plows or rippers to a depth of 20...35 cm, followed by harrowing to a depth of 15...20 cm in one direction (or in cross directions), which increases the thermal insulation effect by 18...30%.. Snow cover the insulated area can be artificially increased by shoveling snow with bulldozers, motor graders, or by retaining snow using shields. Most often, mechanical loosening is used to insulate large areas. Protection of the soil surface thermal insulation materials. The insulating layer can also be made from cheap local materials: tree leaves, dry moss, peat, straw mats, slag, shavings and sawdust. Surface soil insulation is used mainly for small-area excavations.

Soil impregnation with saline solutions proceed as follows. On the surface

sandy and sandy loam soils scatter a given amount of salt ( calcium chloride 0.5 kg/m2, sodium chloride 1 kg/m2), after which the soil is plowed. In soils with low filtering capacity (clays, heavy loams), wells are drilled into which a salt solution is injected under pressure. Due to the high labor intensity and cost of such work, they are usually not effective enough.

Methods for thawing frozen soil can be classified both by the direction of heat propagation in the soil and by the type of coolant used. Based on the first sign, the following three methods of soil thawing can be distinguished.

Soil thawing from top to bottom. This method is the least effective, since the heat source in this case is located in the cold air zone, which causes large heat losses. At the same time, this method is quite easy and simple to implement; it requires minimal preparatory work, and therefore is often used in practice.

Thawing of soil from bottom to top requires minimal energy consumption, since it occurs under the protection of the earth crust and heat loss is practically eliminated. The main disadvantage of this method is the need to perform labor-intensive preparatory operations, which limits the scope of its application.

When the soil thaws in the radial direction heat spreads radially in the ground from vertically installed heating elements immersed in the ground. This method is economic indicators occupies an intermediate position between the two previously described, and for its implementation also requires significant preparatory work.

Based on the type of coolant, the following methods for thawing frozen soils are distinguished:

Fire method. To excavate small trenches in winter, an installation is used (Fig. 1a), consisting of a number of metal boxes in the shape of truncated cones cut along the longitudinal axis, from which a continuous gallery is assembled. The first of the boxes is a combustion chamber in which solid or liquid fuel is burned. Exhaust pipe The last box provides traction, thanks to which combustion products pass along the gallery and heat the soil located underneath it. To reduce heat loss, the gallery is sprinkled with a layer of thawed soil or slag. The strip of thawed soil is covered with sawdust, and further thawing continues in depth due to the heat accumulated in the soil.

Figure 1. Schemes for thawing soil using fire and steam needles: a

By fire; b - steam needles; 1 - combustion chamber; 2 - exhaust pipe; 3 - sprinkling with thawed soil: 4 - steam pipeline; 5 - steam valve; 6 - steam needle; 7 - drilled well; 8 - cap.

Thawing in greenhouses and reverberatory furnaces . Hothouses are boxes open at the bottom with insulated walls and a roof, inside which incandescent coils, water or steam batteries are placed, suspended from the box lid. Reflective furnaces have a curved surface on top, at the focus of which there is an incandescent spiral or an infrared ray emitter, while energy is consumed more economically, and soil thawing occurs more intensively. Hothouses and reverberatory furnaces are powered by a 220 or 380 V power supply. Energy consumption per 1 m 3 thawed soil (depending on its type, humidity and temperature) ranges from 100...300 MJ, while the temperature inside the greenhouse is maintained at 50...60°C.

When thawing the soil with horizontal electrodes on the surface of the soil

They lay electrodes made of strip or round steel, the ends of which are bent by 15...20 cm to connect to the wires (Fig. 2a). The surface of the heated area is covered with a layer of sawdust 15...20 cm thick, which is moistened with a saline solution with a concentration of 0.2...0.5% so that the mass of the solution is not less than the mass

sawdust Initially, the wetted sawdust is a conductive element, since the freezing soil is not a conductor. Under the influence of heat generated in the sawdust layer, it thaws upper layer soil, which turns into a conductor of current from electrode to electrode. After this, under the influence of heat, the top layer of soil begins to thaw, and then the lower layers. Subsequently, the sawdust layer protects the heated area from heat loss into the atmosphere, for which a layer of sawdust is covered plastic film or shields.

Figure 2. Scheme of soil thawing by electric heating: a - horizontal electrodes; b - vertical electrodes; 1 - three-phase electrical network; 2 - horizontal strip electrodes; 3

A layer of sawdust moistened with salt water; 4 - layer of roofing felt or roofing felt; 5 - rod electrode.

This method is used when the depth of soil freezing is up to 0.7 m, the energy consumption for heating 1 m3 of soil ranges from 150 to 300 MJ, the temperature in the sawdust does not exceed 80... 90 ° C.

Thawing soil with vertical electrodes . Electrodes are rods made of reinforcing steel with pointed lower ends. When the freezing depth is more than 0.7 m, they are driven into the ground in a checkerboard pattern to a depth of 20 ... 25 cm, and as the upper layers of the soil thaw, they are immersed to a greater depth. When thawing from top to bottom, it is necessary to systematically remove snow and arrange a sawdust backfill moistened with saline solution. The heating mode for rod electrodes is the same as for strip electrodes, and during a power outage, the electrodes should be further deepened by 1.3 ... 1.5 m. After a power outage for 1 ... 2 days, the thawing depth continues to increase over due to the heat accumulated in the soil under the protection of the sawdust layer. Energy consumption with this method is slightly lower than with the horizontal electrode method.

Using bottom-up heating, before heating begins, it is necessary to drill wells in a checkerboard pattern to a depth 15...20 cm greater than the thickness of the frozen soil. Energy consumption when heating the soil from bottom to top is significantly reduced (50... 150 MJ per 1 m3); the use of a layer of sawdust is not required. When the rod electrodes are buried in the underlying thawed soil and simultaneously installed on the day surface of a sawdust backfill impregnated with a saline solution, thawing occurs from top to bottom and from bottom to top. At the same time, the labor intensity of the preparatory work is significantly higher than in the first two options. This method is used only when it is necessary to urgently thaw the soil.

Thawing the soil from top to bottom using steam or water registers. Regi-

The struts are laid directly on the surface of the heated area cleared of snow and covered with a heat-insulating layer of sawdust, sand or thawed soil to reduce heat loss in the space. Registers thaw soil with a frozen crust thickness of up to 0.8 m. This method is advisable if there are sources of steam or hot water, since installing a special boiler installation for this purpose usually turns out to be too expensive.

Thawing soil with steam needles is one of the effective means, but causes excessive soil moisture and increased heat consumption. A steam needle is a metal pipe 1.5...2 m long, 25...50 mm in diameter. A tip with holes with a diameter of 2...3 mm is mounted on the lower part of the pipe. The needles are connected to the steam line

flexible rubber hoses with taps (Fig. 1b). The needles are buried in wells previously drilled to a depth of 0.7 thaw depth. The wells are covered with protective caps made of wood, covered with roofing steel, with a hole equipped with an oil seal for the passage of a steam needle. Steam is supplied under pressure of 0.06...0.07 MPa. After installing the storage caps, the heated surface is covered with a layer of thermal insulating material (for example, sawdust). To save steam, the heating mode with needles should be intermittent (for example, 1 hour - steam supply, 1 hour - break) with alternate supply of steam to parallel groups of needles. The needles are arranged in a checkerboard pattern with a distance between their centers of 1 ... 1.5 m. Steam consumption per 1 m3 of soil is 50 ... 100 kg. This method requires more heat consumption than the deep electrode method, approximately 2 times.

When thawing the soil with water circulation needles as a heat-

Plants use water heated to 50...60°C and circulating through a closed system “boiler - distribution pipes - water needles - return pipes - boiler”. This scheme ensures the most complete use of thermal energy. The needles are installed in the holes drilled for them. The water needle consists of two coaxial pipes, of which the inner one has open ends at the bottom, and the outer one has pointed ends. Hot water enters the needle inner pipe, and through its lower hole it enters the outer pipe, through which it rises to the outlet pipe, from where it goes through the connecting pipe to the next needle. The needles are connected in series, several in groups, which are connected in parallel between the distribution and return pipelines. Thawing of the soil with needles in which circulates hot water, occurs much slower than around steam needles. After continuous operation of the water needles for 1.5... 2.5 days, they are removed from the soil, its surface is insulated, after which for 1...

After 1.5 days, the thawed zones expand due to accumulated heat. The needles are placed in a checkerboard pattern at a distance of 0.75... 1.25 m from each other and are used for freezing depths of 1 meter or more.

Thawing of soil using heating elements (electric needles) . Heating elements are steel-

pipes about 1 m long with a diameter of up to 50 ... 60 mm, which are inserted into pre-drilled wells in a checkerboard pattern.

A heating element is mounted inside the needles, insulated from the pipe body. The space between the heating element and the walls of the needle is filled with liquid or solid materials that are dielectric, but at the same time transfer and retain heat well. The intensity of soil thawing depends on the surface temperature of electric needles, and therefore the most economical temperature is 60...80°C, but the heat consumption is 1.6... higher compared to deep electrodes.

1.8 times.

When thawing soil with saline solutions Wells are pre-drilled on the surface to the depth to be thawed. Wells with a diameter of 0.3...0.4 m are placed in a checkerboard pattern with a step of about 1 m. A saline solution heated to 80...100°C is poured into them, with which the wells are replenished for 3...5 days. In sandy soils, a well with a depth of 15...20 cm is sufficient, since the solution penetrates deeper due to the dispersion of the soil. Soils thawed in this way do not freeze again after they have been excavated.

Method of layer-by-layer thawing of permafrost soils most appropriate in spring period, when warm air of the surrounding atmosphere can be used for these purposes, warm rainwater, solar radiation. The top thawing layer of soil can be removed using anyearthmoving and transportor leveling machines, exposing the underlying frozen layer, which in turn thaws under the influence of the factors listed above. The soil is cut off at the border between the frozen and thawed layers, where the soil has a weakened structure, which creates favorable conditions for machine operation. In permafrost areas, this method is one of the most economical

useful and common for soil development when planning excavations, trenches, etc.

Method of layer-by-layer freezing of aquifer soils provides for the development

boots before the onset of frost in the top layer of soil lying above the groundwater horizon. When exposed to cold atmospheric air the calculated freezing depth reaches 40...50 cm, they begin to develop the soil in the excavation in a frozen state. Development is carried out in separate sections, between which bridges of frozen soil about 0.5 m thick are left to a depth of about 50% of the thickness of the frozen soil. Jumpers are designed to isolate individual areas from neighboring ones in the event of a breakthrough groundwater. The development front moves from one section to another, while in already developed sections the freezing depth increases, after which their development is repeated. Alternate freezing and development of areas is repeated until the design level is reached, after which the protective bridges are removed. This method makes it possible to develop excavations in frozen soil conditions (without fastening or drainage) that are significantly greater in depth than the thickness of seasonal soil freezing.

Preliminary loosening of frozen soil by means of small-scale mechanization

change when the amount of work is insignificant. For large volumes of work, it is advisable to use mechanical and frost cutting machines.

Explosive loosening method soil is most economical for large volumes of work, significant freezing depth, especially if the energy of the explosion is used not only for loosening, but also for throwing earth masses into a dump. But this method can only be used in areas located far from residential buildings and industrial buildings. When using localizers, the explosive method of loosening soils can also be used near buildings.

Figure 3. Schemes for loosening and cutting frozen soil: a - loosening with a wedge-hammer; b - loosening with a diesel hammer; c - cutting cracks in frozen soil with a multi-bucket excavator equipped with cutting chains - bars; 1 - wedge hammer; 2 - excavator; 3 - frozen layer of soil; 4- guide rod; 5 - diesel hammer; 6 - cutting chains(bars); 7 - multi-bucket excavator; 8 - cracks in frozen soil.

Mechanical loosening of frozen soils used when excavating small pits and trenches. In these cases, frozen soil is loosened to a depth of 0.5...0.7 m hammer and wedge (Fig. 3a), suspended from the boom of an excavator (dragline) - the so-called loosening by splitting. When working with such a hammer, the boom is set at an angle of at least 60°, which ensures a sufficient drop height of the hammer. When using free fall hammers because of dynamic overload quickly wears out the steel rope, trolley and individual machine components; In addition, vibrations from an impact on the ground can have a harmful effect on nearby structures. Mechanical rippers loosen the soil at a freezing depth of more than 0.4 m. In this case, the soil is loosened by chipping or cutting blocks, and the labor intensity of destroying the soil by chipping is several times less than when loosening the soil by cutting. Number of successes

The ditch along one track depends on the depth of freezing, the soil group, the mass of the hammer (2250...3000 kg), the lifting height, it is determined by the hammer of the DorNII design.

Diesel hammers (Fig. 3b) can loosen soil at a freezing depth of up to 1.3 m and, like wedges, are attachments to an excavator, tractor loader and tractor. You can loosen frozen soil with a diesel hammer using two technological schemes. According to the first scheme, a diesel hammer loosens the frozen layer, moving in a zigzag along points located in a checkerboard pattern with a step of 0.8 m. In this case, the crushing spheres from each working stop merge with each other, forming a continuous loosened layer prepared for subsequent development. The second scheme requires preliminary preparation of the open wall of the face, developed by an excavator, after which a diesel hammer is installed at a distance of approximately 1 m from the edge of the face and struck in one place until a block of frozen soil is chipped. Then the diesel hammer is moved along the edge, repeating this operation.

Impact frost breakers (Fig. 4b) work well at low soil temperatures, when it is characterized by brittle rather than plastic deformations, which contribute to its splitting under the influence of impact.

Loosening the soil with tractor rippers. This group includes equipment in which the continuous cutting force of the knife is created due to the traction force of the tractor-tractor. Machines of this type pass frozen soil layer by layer, providing a loosening depth of 0.3...0.4 m for each penetration: Therefore, a frozen layer is developed, previously loosened by machines such as bulldozers. In contrast to impact rippers, static rippers work well at high soil temperatures, when the soil has significant plastic deformations and its mechanical strength is reduced. Static rippers can be trailed or mounted (on the rear axle of the tractor). Very often they are used in conjunction with a bulldozer, which in this case can alternately loosen or develop the soil. At the same time, the trailed ripper is unhooked and the mounted one is raised. Depending on the engine power and the mechanical properties of the frozen soil, the number of ripper teeth ranges from 1 to 5, and most often one tooth is used. For efficient work tractor ripper on frozen soil, it is necessary that the engine has sufficient power (100...180 kW). Loosen the soil with parallel (about 0.5 m) penetrations, followed by transverse penetrations at an angle of 60...90° to the previous ones.

Figure 4. Schemes for developing frozen soils with preliminary loosening: a - loosening with a wedge hammer; b - tractor vibro-wedge ripper; 1 - dump truck; 2 - excavator; 3 - hammer wedge; 4 – vibrating wedge.

Frozen soil, loosened by cross penetrations of a single-column ripper, can be successfully developed with a tractor scraper, and this method is considered very economical and successfully competes with the drilling and blasting method.

When developing frozen soils with preliminary cutting into blocks, slits are cut in the frozen layer (Fig. 5), dividing the soil into separate blocks, which are then removed with an excavator or construction cranes. The depth of the cracks cut in the frozen layer should be approximately 0.8 of the freezing depth, since the weakened layer at the border of the frozen and thawed zones is not an obstacle to excavation. In areas with permafrost soils, where there is no underlying layer, the block mining method is not used.

Figure 5. Schemes for developing frozen soils using the block method: a, b - small-block method; c, d - large-block; 1 - removal of snow cover; 2, 3 - cutting blocks of frozen soil with a bar machine; 4 - development of small blocks with an excavator or bulldozer; 5 - development of thawed soil; 6 - development of large blocks of frozen soil with a tractor; 7 - the same, with a tap.

The distances between the cut slots depend on the size of the excavator bucket (the size of the blocks should be 10... 15% less than the width of the excavator bucket). Blocks are shipped by excavators with buckets with a capacity of 0.5 m and above, equipped primarily with a backhoe, since unloading blocks from a bucket with a straight shovel is very difficult. To cut cracks in the ground, various equipment installed on excavators and tractors is used.

You can cut cracks in frozen soil using bucket wheel excavators, in which the bucket rotor is replaced by milling discs equipped with teeth. For the same purpose, disc milling machines are used (Fig. 6), which are attachments to the tractor.

Figure 6. Disc-milling earthmoving machine: 1 - tractor; 2 - transmission and control system for the working body; 3 - working part of the machine (mill).

It is most effective to cut cracks in frozen soil using bar machines (Fig. 5), the working element of which consists of a cutting chain mounted on the base of a tractor or trench excavator. Bar machines cut slots with a depth of 1.3 ... 1.7 m. The advantage of chain machines compared to disk machines is the relative ease of replacing the most quickly wearing parts of the working body - replaceable teeth inserted into the cutting chain.

Sale with delivery of hot sand in Moscow to warm up the soil or soil in winter.

Bulk density: 1.5 (t/m3)

Payment by bank transfer including VAT. Prepayment 100%.

Delivery the next day after payment. The travel time of a hot sand dump truck is from 1 to 3 hours. Delivery in Moscow is carried out in the first half of the day.

Characteristics:

GOST 8736-93, TU 400-24-161-89
Class: II
Size module: from 1.5 Mk to 2.8 Mk
Filtration coefficient: from 2 m/day to 9.5 m/day
Content of dust and clay particles: up to 10%
Clay content in lumps: up to 5%
Color: brown, yellow, light yellow, brown, light brown
Geological deposits: Moscow region, Vladimir region, Kaluga region.
Bulk density: 1.5 g/cm3. (t/m3)

Origin: sand quarries.

Application area: for heating the top layer of earthen soil in winter when laying and repairing heating networks, etc.

Extraction method: It is mined in open-pit sand quarries and is achieved by heating in production furnaces to a temperature of 180 to 250 degrees Celsius.

Additional information about hot sand in construction:

Hot sand in winter serves as an indispensable material for warming the soil or any other top soil when sub-zero temperatures when laying various communications underground. When using hot sand, the effect of heated soil is achieved and it becomes more convenient for work, especially since there is a high probability of damage to pre-laid communications, for example, heating networks, etc.

Hot sand is a seasonal product; it is relevant only in sub-zero temperatures. During production, it reaches an average temperature of 220 degrees Celsius, and as a result, all moisture evaporates from it and it becomes completely stuck through. Although this quality of sand is rather a quality indicator for the production of dry mixtures, it cannot be applied to hot sand or improved its performance for higher heat transfer. This is rather simply the result of heating at high temperatures. Hot sand is a high-quality product, since in addition to the fact that the raw material for it is high-quality quarry sand of class 2, it is also heated and dried and complies with TU 400-24-161-89.

When ordering hot sand in an amount of 10 m3, its temperature at the time of delivery to the object of use practically does not change and it retains its high quality properties. As a rule, the practice of delivering and using hot sand on the eve of the day of work is used, for example, in the evening of the day after which the work is being carried out. Ten hours is enough to warm up the top layer of soil and prepare it for further work, while the sand will not freeze during this period of time.

Our country is located in northern latitudes. The winter period with negative temperatures takes a lot of time from builders. However, you can’t stop capital construction, if you warm up the soil. This procedure is becoming increasingly popular. In this article we will talk about the main methods of heating the soil.

Why is soil heating needed in winter?

When construction is carried out within the city, it becomes dangerous to remove frozen soil using demolition equipment. You can easily damage underground communications, of which there are so many in the city: cable lines, water pipelines, gas pipelines. In such places, soil often has to be removed manually. In winter, frozen soil cannot be removed from the trench with shovels. Therefore, soil heating is ordered immediately before the start of construction work. At the same time, heating of the concrete after pouring the foundation is ordered to ensure its hydration and proper hardening.

What are the different ways to warm up the soil?

There are many ways to warm the ground at a construction site. They differ not only in costs, but also in efficiency. We list the main ones:

Warming up with hot water. This method is suitable for defrosting small areas of land. Labyrinths of flexible hoses are laid over the area, which are covered with polyethylene or any heat insulator. Water heated to 70-90 degrees Celsius is released through the sleeves. For this, a heat generator or pyrolysis boiler is used. The defrosting speed is no more than 60 cm per day. Disadvantages: high cost of equipment and low warm-up speed.
Warming up with steam and steam needles. Wells with a depth of one and a half to two meters are drilled on the site for special metal pipes diameter up to 50 mm. These so-called needles have holes at the ends no larger than 3 mm. The pipes are staggered every 1-1.5 meters. Saturated water vapor is supplied to the needles (temperature - more than 100 degrees Celsius, pressure - 7 atmospheres). This method is used only for deep pits - more than 1.5 meters. Disadvantages are complex preparatory work, the release of large volumes of condensate and the need for constant monitoring of the process.
Warming up with heating elements. This method is similar to the steam needles used as a tool. Pipes with a length of 1 meter and a diameter of up to 60 mm are also used. They are installed in drilled wells at the same distance. Inside the pipes there is a liquid dielectric with high thermal conductivity. The heating elements are connected to the electrical network. Electricity consumption per 1 cubic meter meter of land - 42 kWh. Disadvantages: high costs.
Warming up with electric mats. The method involves the use of infrared mats, which work on the principle of similar mats for “warm floors”. Electromats heat the soil to a temperature of 70 degrees. The heating depth is no more than 80 cm in 32 hours. Electricity consumption - 0.5 kWh per 1 square meter. Disadvantages - fragile material, need for constant monitoring.
Heating with ethylene glycol using a Waker Neuson unit. The equipment runs on diesel fuel. From this point of view, it is autonomous and does not depend on communications (electricity). A hose is laid out like a snake across the area of the site, through which heated ethylene glycol will circulate. This liquid has the highest thermal conductivity and a higher boiling point than water. The hoses are covered with thermal insulation mats. One installation allows you to defrost 400 square meters to a depth of 1.5 meters in 8 days.

Our company offers soil and concrete heating services using the Waker Neuson installation. This method is considered the most effective in terms of cost per area and defrosting time.

A significant part of Russia's territory is located in areas with long and severe winters. However, construction is underway here all year round, due to which approximately 20% of the total volume of excavation work has to be carried out when the soil is frozen.

Frozen soils are characterized by a significant increase in the labor intensity of their development due to increased mechanical strength. In addition, the frozen state of the soil complicates the technology, limits the use of certain types of earthmoving (excavators) and earthmoving and transport (bulldozers, scrapers, faders) machines, reduces the productivity of vehicles, and contributes to the rapid wear of machine parts, especially their working parts. At the same time, temporary excavations in frozen soil can be developed without slopes.

Depending on specific local conditions, soil development in winter conditions is carried out using the following methods: 1) protecting the soil from freezing and subsequent development using conventional methods, 2) developing soil in a frozen state with preliminary loosening, 3) direct development of frozen soil, 4) thawing of the soil and its development in a thawed state.

The soil is protected from freezing by loosening the surface layers, covering the surface with various insulation materials, and impregnating the pound with saline solutions.

Loosening of the soil by plowing and harrowing is carried out in an area intended for development in winter conditions. As a result, the top layer of the pound acquires a loose structure with closed voids filled with air, which has sufficient thermal insulation properties. Plowing is carried out with factor plows or rippers to a depth of 20...35 cm, followed by harrowing to a depth of 15...20 cm in one direction (or in cross directions), which increases the thermal insulation effect by 18...30%.

Covering the soil surface is carried out with thermal insulation materials, preferably from cheap local materials: tree leaves, dry moss, peat fines, straw mats, slag, fumes and sawdust, laid in a layer of 20...40 cm directly by the pound. Surface insulation of the pound is used mainly for small-area recesses.

Loosening of frozen soil with subsequent development by earth-moving or earth-moving machines is carried out using the mechanical or explosive method.

Mechanical loosening is based on cutting, splitting or chipping a layer of frozen soil under static or dynamic influence.

Static impact is based on the impact of continuous cutting force in frozen soil by a special working body - a tooth. For this purpose, special equipment is used, in which the continuous cutting force of the tooth is created due to the traction force of the tractor-tractor. Machines of this type carry out layer-by-layer penetration of frozen soil, providing a loosening depth of about 0.3...0.4 m for each penetration. The soil is loosened by parallel (about 0.5 m) penetrations, followed by transverse penetrations at an angle of 60...90 ° to the previous ones. Ripper productivity is 15...20 m3/h. Hydraulic excavators with a working body - a ripper tooth - are used as static rippers.

The possibility of layer-by-layer development of frozen pound makes static rippers applicable regardless of the depth of freezing.

The dynamic impact is based on the creation of impact nuclei on the open surface of the frozen pound. In this way, the pound is destroyed with free-fall hammers (splitting loosening) or directional hammers (chip loosening). A free-fall hammer can take the form of a ball or wedge weighing up to 5 tons, suspended on a rope from the boom of an excavator and dropped from a height of 5...8 m. Balls are recommended for loosening sandy and sandy loam pounds, and wedges for clayey ones (at a freezing depth of 0 .5...0.7 m).

Diesel hammers are widely used as directional hammers, used as attachments to an excavator or tractor. Diesel hammers allow you to destroy a pound to a depth of up to 1.3 m.

Explosion loosening is effective at freezing depths of 0.4...1.5 m or more and with significant volumes of frozen pound development. It is used mainly in undeveloped areas, and in limitedly built-up areas - with the use of shelters and explosion localizers (heavy slabs). When loosening to a depth of 1.5 m, borehole and slot methods are used, and at greater depths, borehole or slot methods are used. Slots at a distance of 0.9...1.2 m from one another are cut with slot-cutting machines milling type or bar machines. Of the three adjacent slits, one middle one is charged; the outer and intermediate slits serve to compensate for the shift of the frozen pound during an explosion and to reduce the seismic effect. The cracks are charged with elongated or concentrated charges, after which they are filled with sand. During explosion, the frozen pound is completely crushed without damaging the walls of the pit or trench.

Direct development of frozen soil (without preliminary loosening) is carried out by two methods: block and mechanical.

The block method is based on the fact that the solidity of frozen soil is broken by cutting it into blocks, which are then removed with an excavator, construction crane or a tractor. Cutting into blocks is carried out in mutually perpendicular directions. For shallow freezing depths (up to 0.6 m), it is enough to make only longitudinal cuts. The depth of the cracks cut in the frozen layer should be approximately 80% of the freezing depth, since the weakened layer at the border of the frozen and thawed zones is not an obstacle to the separation of blocks from the massif. The distance between the cut slots depends on the size of the edge of the excavator bucket (the size of the blocks should be 10...15% less than the width of the excavator bucket). For unloading blocks, excavators with buckets with a capacity of 0.5 m3 and above, equipped primarily with a backhoe, are used, since unloading blocks from a bucket with a straight shovel is very difficult.

The mechanical method is based on force (sometimes in combination with shock or vibration) impact on the frozen soil mass. It is implemented by using both conventional earth-moving and earth-moving and transport machines, and machines equipped with special working parts.

Conventional machines are used for shallow freezing depths: front and backhoe excavators with a bucket capacity of up to 0.65 m3 - 0.25 m, the same with a bucket capacity of up to 1.6 m3 - 0.4 m, dragline excavators - up to 0.15 m, bulldozers and scrapers - 0.05...0.1 m.

To expand the scope of use of single-bucket excavators in winter, the use of special equipment has begun: buckets with vibro-impact active teeth and buckets with a gripping-pincer device. Due to the excess cutting force, such single-bucket excavators can develop an array of frozen pound layer by layer, combining the processes of loosening and excavation into a single one.

Layer-by-layer development of the soil is carried out with a specialized earth-moving and milling machine, which removes “chips” up to 0.3 m thick and 2.6 m wide. The developed frozen soil is moved using bulldozer equipment included in the machine.

Thawing of frozen soil is carried out using thermal methods, which are characterized by significant labor and energy intensity. That's why thermal methods used only in cases where others effective methods unacceptable or unacceptable, namely: near existing underground communications and cables, if it is necessary to thaw frozen foundations, during emergency and repair work, in cramped conditions (especially in conditions of technical re-equipment and reconstruction of enterprises).

Methods for thawing frozen soil are classified both according to the direction of heat propagation in the soil and according to the type of coolant used.

Based on the direction of heat propagation into the soil, the following three methods of soil thawing can be distinguished.

The method of thawing the soil from top to bottom is ineffective, since the heat source is located in the cold air zone, which causes large heat losses. At the same time, this method is quite easy and simple to implement, since it requires minimal preparatory work.

The method of thawing the soil from the bottom up requires minimal energy consumption, since thawing occurs under the protection of the ice-earth crust and heat loss is practically eliminated. The main disadvantage of this method is the need to perform labor-intensive preparatory operations, which limits the scope of its application.

When the soil thaws in the radial direction, heat spreads in pounds radially from vertically installed defrosting elements, rated in pounds. This method, in terms of its economic indicators, occupies an intermediate position between the two previously described, and for its implementation it also requires significant preparatory work.

Based on the type of coolant, the following main methods of thawing frozen soils are distinguished.

The fire method is used to excavate small trenches in winter. To do this, it is economical to use a link unit consisting of a number of metal boxes in the form of truncated cones cut along the longitudinal axis, from which a continuous gallery is assembled. The first of the boxes is a combustion chamber in which solid or liquid fuel is burned. The exhaust pipe of the last box provides draft, thanks to which combustion products pass along the gallery and heat the soil located underneath it. To reduce heat loss, the gallery is sprinkled with a layer of thawed soil or slag. The strip of thawed soil is covered with sawdust, and further thawing continues in depth due to the heat accumulated in the soil.

The electric heating method is based on passing current through the heated material, as a result of which it acquires a positive temperature. The main technical means are horizontal or vertical electrodes.

When thawing the soil with horizontal electrodes, electrodes made of strip or round steel are laid on the surface of the soil, the ends of which are bent by 15...20 cm to connect to the wires. The surface of the heated area is covered with a layer of sawdust 15...20 cm thick, which is moistened with a saline solution with a concentration of 0.2...0.5% so that the mass of the solution is not less than the mass of sawdust. Initially, the wetted sawdust is a conductive element, since frozen soil is not a conductor. Under the influence of heat generated in the sawdust layer, the top layer of soil thaws, which turns into a conductor of current from electrode to electrode. After this, under the influence of heat, the next layer of soil begins to thaw, and then the underlying layers. Subsequently, the sawdust layer protects the heated area from heat loss into the atmosphere, for which the sawdust layer is covered with roofing felt or shields. This method is used when the freezing depth of a pound is up to 0.7 m, the energy consumption for heating 1 m3 of soil ranges from 150 to 300 MJ, the temperature in the sawdust does not exceed 8O...9O°C.

Thawing of soil with vertical electrodes is carried out using reinforcing steel rods with pointed lower ends. At a freezing depth of 0.7 m, they are driven into the ground in a checkerboard pattern to a depth of 20...25 cm, and as the upper layers of soil thaw, they are immersed to a greater depth. When thawing from top to bottom, it is necessary to systematically remove snow and arrange a sawdust backfill moistened with saline solution. The heating mode for rod electrodes is the same as for strip electrodes, and during a power outage, the electrodes should be sequentially deepened as the soil warms up to 1.3...1.5 m. After a power outage for 1...2 days, the depth thawing continues to increase due to the heat accumulated in the soil under the protection of the sawdust layer. Energy consumption with this method is slightly lower than with the horizontal electrode method.

Using bottom-up heating, before heating begins, it is necessary to drill wells located in a checkerboard pattern to a depth 15...20 cm greater than the thickness of the frozen pound. Energy consumption when heating a pound from bottom to top is significantly reduced, amounting to 50...150 MJ per 1 m3, and the use of a layer of sawdust is not required.

When the rod electrodes are buried in the underlying melt pound and at the same time a sawdust backfill impregnated with a saline solution is placed on the day surface, thawing occurs both in the direction from top to bottom and from bottom to top. At the same time, the food intensity of the preparatory work is significantly higher than in the first two options. This method is used only in exceptional cases when it is necessary to urgently thaw the pound.

Steam thawing is based on the injection of steam into a pound, for which special technical means- steam needles, which are a metal tube up to 2 m long, with a diameter of 25...50 mm. A tip with holes with a diameter of 2...3 mm is mounted on the lower part of the pipe. The needles are connected to the steam line by flexible rubber hoses with taps. The needles are buried in wells that are pre-drilled to a depth equal to 70% of the thawing depth. The wells are closed with protective caps equipped with seals for the passage of a steam needle. Steam is supplied under pressure of 0.06...0.07 MPa. After installing the accumulated caps, the heated surface is covered with a layer of thermal insulating material (for example, sawdust). The needles are arranged in a checkerboard pattern with a distance between centers of 1...1.5 m. Steam consumption per 1 m3 lb is 50...100 kg. This method requires heat consumption approximately 2 times greater than the deep electrode method.

Warming the earth with its warmth... (Part 1)

Equipment and methods for heating frozen soils during excavation work

As you know, in winter the soil sometimes freezes so much that even an excavator and hydraulic hammer cannot handle it. Moreover, in populated areas There are underground communications in the ground that can be damaged by impact impacts on the ground. Therefore, frozen soil must be pre-warmed. There are a number of ways to warm up frozen soil. Each of them has its own advantages and disadvantages.

Methods for thawing frozen soil are classified according to the direction of heat supply to the soil and the type of coolant used.

Thawing from top to bottom. This method is the least effective, since the heat source in this case is located in the cold air zone, which causes large heat losses. At the same time, it is quite easy and simple to implement; it requires minimal preparatory work, and therefore is often used in practice.

Defrosting from bottom to top involves drilling wells into which heat sources are lowered. Energy consumption in this case is minimal, since due to the soil layer there is practically no heat loss. Some experts even believe that it is not necessary to insulate the treated area on top with a layer of sawdust and other materials. The main disadvantage of this method is the labor-intensive preparatory operations, which limits the scope of its application.

Defrosting in a radial direction. In this case, heat spreads in the ground perpendicularly from energy sources vertically immersed in the ground. This method, in terms of economic indicators, occupies an intermediate position between the two previously described, and also requires significant preparatory work to implement.

Regardless of the method adopted, the heated surface is first cleared of snow, ice and top layers of the base (asphalt, concrete).

Thermoelectric mats

Thermoelectric mats (thermomats) are infrared heaters, multifunctional and environmentally friendly auxiliary construction equipment, they allow you to effectively heat the soil and hardening concrete with little energy consumption, maintain the set temperature automatically, and some models can be used to melt snow and ice. The design of thermomats includes a heating film that emits heat in the infrared range, with thermal insulation, which is a multilayer “sandwich” of polypropylene or polyethylene foam 6–10 mm thick, limiters to maintain a constant temperature and a dirt- and water-resistant PVC shell with hermetically sealed seams, resistant to adverse conditions. atmospheric influences. They are produced in the form of rectangular panels of various sizes and rolls of considerable length.

Possibilities of thermomats. Many Western and domestic experts believe that heating the soil with thermoelectric and thermal insulation mats is optimal technology for thawing large areas of frozen soil and ice. They can operate from single-phase power sources with a voltage of 220 V. They work better than the sun on a spring day - 24 hours, 7 days a week. They are capable of heating soil to temperatures 50–80 °C above ambient temperature and warming up heavily frozen soil to a depth of 450–800 mm in 20–72 hours of operation, depending on the air temperature and soil properties. Snow and ice turn into water, which is absorbed into the soil and thaws the underlying layers of soil. They are capable of defrosting frozen sewer pipes at a depth of up to 2.5 m. The permissible operating temperature of thermomats can be down to –35 °C. The specific power emitted by thermomats can reach several hundred watts per 1 m2. Due to the penetrating properties and directed action of infrared radiation, as well as contact heat transfer from the surface of the thermomat, soil heating occurs with high efficiency simultaneously to the entire freezing depth.

Company "Thermal systems"(Moscow), part of the AKKURAT Group of Companies, is engaged in the development, testing and production of TEM thermoelectric mats to accelerate the hardening of concrete and to warm up the soil. In addition, thermomats are also used to perform other tasks, for example, heating containers, heating masonry, etc.

Thermoelectric mats are manufactured according to our own patent using high-quality infrared film Marpe Power 305 with increased power (400, 600 and 800 W/m2), which is produced by the South Korean company Green Industry Co. Supply voltage 220 V/ 50 Hz. Operation is allowed at ambient temperatures from –60 to +40 °C and relative humidity up to 100%.

The main condition for proper operation of thermomats is a tight fit work surface thermomat to the heated object (concrete or soil). The time to gain critical strength (70%) for a concrete slab with a thickness of 200 mm is about 12 hours; Warming up time for frozen soil is from 20 to 36 hours.

Test results. The technical literature provides descriptions of tests of one of the models of thermomats with dimensions of 1.2x3.2 m and a power of 800 W/m 2. The experiment was carried out at the end of winter, during the period of greatest soil freezing. Heating of the soil by thermomats occurred automatically at an air temperature of –20 °C, an initial soil temperature of –18 °C, the top 20 cm layer of soil consisted of a mixture of clay, sand and slag, followed by pure clay. The area was cleared of snow, the surface was leveled as much as possible, and plastic film was laid on it. Next, the thermomats were placed one next to the other without overlap and connected to the power supply using a “parallel” circuit. In the first hours, all the released heat was absorbed by the soil, and the thermomats worked without turning off, then, as the soil surface warmed up to 70 °C, the thermomats began to turn off, and when the temperature of the thermomat dropped to 55–60 °C, it turned on again. The warming up time is influenced by the initial conditions (air and soil temperature) and soil properties (thermal conductivity, humidity). Tests have shown that to warm up this soil to a depth of 600 mm, it takes from 20 to 32 hours.

Thermal mats create a stable heat flow, which is a necessary condition high-quality hardening of concrete in winter and summer and eliminates the appearance of temperature cracks. Branded concrete gains the strength in 11 hours that it would have acquired in 28 days under natural conditions. A high speed of concrete setting is achieved due to the penetration of infrared rays into the thickness of the concrete mass.

Application. The mats are rolled out from rolls and connected to a power source. To increase the efficiency of their operation, it is recommended to lay thermal insulating protective mats on top to retain heat and protect from wind. To avoid overheating and burning out of the thermomat, it is necessary to ensure a tight fit of the thermomat to the heated surface. It is not allowed to place any heat-insulating materials between the mat and the heated object that would prevent the transfer of heat to the object.

LLC "Plant "UralSpetsGroup"(Miass) offers thermomats with built-in temperature limit sensors for heating concrete and soil with a power of 400 and 800 W/m 2, respectively. Thermal mats can consist of several independent sections. Each section has its own thermostat-limiter and maintains the heating temperature in a certain range.

Due to the uniform distribution of heat on the heated surface and automatic control temperature significantly accelerates the growth of concrete strength. The curing time for concrete to reach grade strength ranges from 10 hours to 2 days. The heating temperature of the mats is not higher than +70 °C. Operating conditions: ambient temperature from –40 to +40 °C, relative humidity up to 100%.

Advantages of thermomats. The equipment does not require preliminary preparation and is completely ready for use; relatively low cost; ease of setup and maintenance; light weight and ease of use, no special skills are required from workers; high efficiency and low energy consumption, for example, 0.5 kWh per 1 m 2. Thermoelectromats are completely safe. Each segment of the thermomat has a temperature limiter; the temperature will not rise above the set value. The equipment does not pollute environment. At the customer's request, thermomats can be produced with individual power parameters and dimensions.

Disadvantages of thermomats. The need to provide power supply and constant monitoring of equipment operation; lack of anti-vandal protection, relative instability to damage.

Hydraulic stations for soil heating

If you need to warm the soil in winter by large area, for example, for the installation of a concrete pad of 400 m2 or more, in the usual ways- thermomats, infrared emitters, heat guns, it is unlikely that it will be possible to heat such a mass of earth in such an area. Most likely, the technology of warming the earth using the greenhouse effect, which is created by hydraulic stations, will be effective here. Currently, Western companies widely use the technology of defrosting soils using hydraulic stations in winter for excavation and concrete work. Compact hydraulic stations for heating the soil have appeared on the world market construction equipment about 15 years ago.

Installation design and operation. The installation itself is a mobile mini-boiler room. The trailer on which the hydraulic station is located is installed as close as possible to the area that is to be warmed up.

The heated surface is cleared of snow. Thorough cleaning will reduce the defrosting time by 30%, save fuel, and get rid of dirt and excess melt water, which complicates further work. The boiler is turned on, in which the coolant is heated. Water is most often used as a coolant, but in the West a water-glycol or propylene-glycol mixture is also used. Maximum heating temperature of the coolant in modern installations(depending on the manufacturer) is in the range of 75–90 °C. The digital thermostat allows the operator to simply adjust the temperature of the coolant. The heating boiler is equipped with a burner that runs on gas or diesel fuel. The coolant heated to a given temperature enters a thermally insulated container. From the container, the coolant is pumped into the heating hoses using a pump.

The heating hoses are unwound from the reel. It is recommended to lay them in a “snake” pattern in 2–4 rows, depending on the intensity of heating required. How less distance between turns (for example, 450 mm), the less time it will take to warm up the surface. Depending on the inter-hose distance, the required area and heating rate can be achieved. The inlets and outlets of the hoses are connected to the distribution manifold of the station so that the coolant circulates through them along closed loop. In principle, hoses can be laid in any pattern; there are also no restrictions on the shape and topography of the heated surface.

Diesel station for soil defrosting and concrete heating SRGPB.SI.350 produced JSC "SI"(Moscow city). Thermal power – 31 kW/h. Thermal efficiency is 85%. Can operate continuously for 120 hours. The volume of the coolant system is 190 liters. Heating system operating temperature: 37–82 °C. Working pressure in the heating system: 4.7–6.2 bar. Heating hose length – 360 m. Circulation pump capacity – 1010 l/h. The defrosting and heating area is from 104 to 210 m2. The defrosting area with an additional enlarged hose storage reel and pump is from 310 to 620 m2. Allows you to warm up soil up to 400 mm in depth in 24 hours. Mounted on a single-axle trailer chassis. The weight of the unit, filled with fuel, is 1402 kg.

The hoses are reinforced with synthetic fiber and have exceptional flexibility and tensile strength. The serviceability and readiness of the equipment for operation is monitored by built-in sensors. The hoses and the heated area must be covered with a vapor-proof or overlapping polyethylene film (especially important when working with concrete) and heat-insulating mats (insulation) in order to create “ Greenhouse effect» and reduce heat loss in ambient air. The more thoroughly the heated surface is insulated, the less time it will take to warm up the soil. The film will not allow the heated water to evaporate. Melt water will melt the ice in the lower layers of the soil.

Preheating time only takes about 30 minutes. The tap opens and the heating starts! In hydraulic stations of some manufacturers, it is possible, if necessary, to increase the nominal heating area of the soil several times by connecting an additional pump and additional hoses. Frozen soil is heated in a relatively short time - 20–30 hours, but if necessary, continuous operation of such installations is possible for up to 60–130 hours. Such an installation has efficiency. up to 94%, that is, almost all the heat generated by the installation goes to warming the soil. average speed soil defrosting similar method is 300–600 mm in depth per day. However, with more dense packing of the heating hoses and careful thermal insulation, the rate of defrosting can be increased.

Other possible applications. Soon after the use of this technology began, it turned out that hydraulic stations also help speed up the hardening process of concrete in winter, preventing moisture in concrete from turning into ice even at temperatures from -30 to -40 ° C. Concrete requires heat to harden: the warmer the concrete is, the sooner it will harden; the optimal temperature for hardening is from +20 to +25 ° C. In severe frost, concrete will harden for a very long time and lose quality. In addition, heating hydraulic stations can be used to heat greenhouses and flower beds, heat rooms, prevent icing of football fields, etc.

In Russia, hydraulic installations for heating the soil are widely used for work on large sites. Wacker Neuson E350 And E700, HSH 700G. The units are certified in Russia and do not require special permits for the operator.

Hydraulic station for surface heating Wacker Neuson HSH 350 has a mass (with fuel) of 1500 kg. Heater capacity (gross) 30 kW. At ideal conditions efficiency can reach 94%. Hose length – 350–700 m.

The HSH series installation can defrost frozen soil and also process concrete even at sub-zero temperatures. Possibility of continuous operation - up to 63 hours. When using additional equipment, it is possible to ensure thawing of soil up to 300 m2 and warm up to 612 m2 of concrete. The HSH device is trailer mounted.

Advantages and disadvantages. The advantages of this technology over other methods are: the ability to heat large areas of soil; ease of operation, maintenance and storage of equipment; the use of equipment does not require specific knowledge, skills and long-term training of personnel; autonomy, mobility and versatility of equipment; stability of results during work; minimal labor and material costs for preparing the heated surface; environmental friendliness and safety - there is no danger of damage electric shock and hot coolant, does not create magnetic fields, the heating hoses are completely sealed.

The disadvantages include high cost equipment (2–3 million rubles), the need for the constant presence of an operator during work.

If a hydraulic station is required for a one-time use or not often, you can rent it. Thanks to the above advantages, the money spent on rent will pay off very quickly. Usually, as soon as a company tries to use such a hydraulic station once, it becomes an adherent of the technology of hydraulic soil heating.

Warmhouse/tent and heating equipment

Warming up with hot air. Quite simple and available method heating the soil - using hot air - allows you to defrost the soil in the coldest time. Snow must first be removed from the heated area. A temporary structure is erected above the site - a greenhouse or a tent. Teplyak is a temporary frame-tent construction shelter for hydro- and thermal insulation. Used when performing construction work. Diesel, gas or electric is installed inside heat gun, gas-burner or stove. The air in the greenhouse/tent can heat up to 50–65 °C. The walls and roof of the greenhouse/tent can be covered with existing heat-insulating materials or even spruce branches from the forest.

In our country, heat guns are produced under the brand Hyundai. For example, Hyundai heat gun H-HG7-50-UI712 with heating element heating element with a power of 4.5 kW. The unit has operating modes: ventilation, intensive and economical heating. The air temperature at the outlet compared to the inlet increases by 32 °C. Productivity – 420 m3/h of air. Duration of operation/pause – 22/2 hours. There is an overheat protection sensor.

Advantages. Constructing such a temporary room or deploying such an installation is much simpler and requires less labor than other types of soil heating equipment. Simultaneously with defrosting, this installation dries the soil, and it becomes easier to dig. Western manufacturers of such equipment claim that their installations heat and dry the soil twice as fast as when using hydraulic stations with hoses through which hot coolant circulates.

Flaw. Weak thermal insulation, hence large heat losses; air heat guns transfer only about 15% of thermal energy to the ground.

Italian company Master Climate Solutions(part of the Dantherm Group) produces air heaters under the brand at a plant in Italy MASTER. Diesel heat guns with direct and indirect heating, as well as gas and electric heat guns. Some of the guns with diesel heating are equipped with a special socket thermostat TN-1, which is installed directly on the product, or with a TN-2 thermostat, which is connected using a cable. The units are capable of continuously operating for a long time with almost 100% efficiency.

For example, direct heating diesel heat gun MASTER B 150 CED with a power of 44 kW, it develops an air flow of 900 m 3 / h, fuel consumption is 3.7 kg / h, the air outlet temperature is 300 ° C, and the installation weight is 30.3 kg. Operates without refueling for 13 hours. Equipped with a device automatic control combustion with photocell and burner and heater safety system. The outer casing of the heater remains cold.

Open flame. The use of an open flame to defrost soil, or the “fire method,” is based on thawing the soil by burning solid or liquid fuel in a unit consisting of a gallery of metal boxes in the shape of a semicircle or truncated cones.

The boxes can be made from sheet steel 1.5–2.5 mm thick or from improvised materials, for example, from metal barrels cut to length. The first of the boxes acts as a combustion chamber in which any solid or liquid fuel is burned. For example, a gas burner (nozzle) is installed in the combustion chamber, connected by a hose to gas cylinder. The gas burner used for this purpose can simply be a piece of steel tube with a diameter of 18 mm with a flattened cone. The exhaust pipe of the last box provides draft, thanks to which combustion products pass along the gallery and heat the soil located underneath it. To reduce heat losses, the gallery is insulated with a layer of thawed soil up to 100 mm thick, slag or other materials.

There are many modern burners on sale now. For example a burner Giersch RG 20-Z-L-F(Germany) with two-stage power regulation 40–120 kW. Operates on natural and liquefied gas. Power supply – 220 V, maximum current consumption – 2.6 A. Electric motor power – 180 W. Built-in sound insulation, there is an air pressure control sensor. Can also be installed in a vertical position.

With a box length of 20–25 m, the installation makes it possible to heat the soil at a depth of 0.7–0.8 m per day. Experts provide the following data: diesel fuel consumption for heating 1 m 3 of soil is 4–5 kg. Heating with a flame is recommended to be carried out for 15–16 hours. Then, after dismantling the boxes, the strip of thawed soil is covered with sawdust so that thawing continues deeper due to the transfer of heat accumulated in the soil.

Flaws this technology: bulky, inconvenient equipment for transportation; the method can be used to excavate only relatively narrow and shallow trenches, since it allows only small areas to be heated. Heating a large area with such burners will be very expensive. The defrosting process takes a long time. It is necessary to carry out auxiliary work on the arrangement (and disassembly) of the structure. It is necessary to constantly monitor the process and compliance with safety regulations. Large heat losses, low fuel efficiency. Harmful emissions from burned fuel, resulting in a ban on the use of this method in cities

Advantages. There are not many of them. You can assemble such an “installation” from scrap materials and heat it with construction waste - scraps of boards, flammable garbage. The advantages of using gas compared to diesel burners are lower price and less harmful emissions and smoke.

Universal gas burner Roca CRONO-G 15G(Spain) runs on liquefied and natural gas and is extremely safe to operate. Before ignition, the combustion chamber is purged with air. Single-stage, two-stage or modulating power control is possible. Power – 65–189 kW. Fuel consumption – 6.5–18.9 kg/h. Electric motor power – 350 W. Power supply– 220 V. Weight – 15 kg.

Reflective furnaces. As experience has shown, when repairing municipal utility networks, the most convenient and fastest method is to warm frozen soil with reflective stoves, which are suspended from the inside to the roof of the greenhouse - a box open at the bottom with insulated walls and roof.

Reflective furnaces have a parabolic-shaped reflector on top made of aluminum, duralumin or chrome-plated steel sheet 1 mm thick. At the focus of the parabola, which is located at a distance of 60 mm from the reflector, there is a source of heat rays: an electric incandescent coil, a water or steam battery. The reflector focuses heat rays on the underlying area of the ground, due to this energy is spent more economically, and the soil thaws more intensively than when heated warm air. The top of the furnace is covered with a steel casing that protects the reflector from mechanical damage. There is a layer of air between the casing and the reflector, which improves the thermal insulation of the furnace. The incandescent spiral is made of nichrome or fechral wire with a diameter of 3.5 mm, wound in a spiral on an insulated asbestos steel pipe. Nichrome (Ni-Cr and Ni-Cr-Fe) received its name from the nickel (“ni”) and chromium (“chromium”) in its composition, and fechral (Fe-Cr-Al) is named after the first letters of the main elements (“fe ", "hr", "al"). On the modern market, fechral is at least 3–5 times cheaper than nichrome. However, nichrome is able to withstand a greater number of on-off cycles of heating elements before they burn out.

The use of heaters and reflectors. When using reflex furnaces, it is necessary to ensure safe working conditions. The heating area must be fenced, the contact terminals for connection by wire are closed, and the leak spirals must not touch the ground.

Hothouses and reverberatory furnaces can be powered from a 380 or 220 V electrical network. If the heating elements are powered from a three-phase electricity source, the heating elements are connected in groups of three according to a “star” or “delta” circuit, depending on the voltage of the power source and voltage for which the heating elements are designed (“triangle” - if the heating elements are designed for a voltage of 380 V, “star” - if for 220 V). To operate a complex of three installations, a source of electricity with a capacity of about 20 kW/h is required. Experts say that the energy consumption for thawing 1 m 3 of soil for a period of 6–10 hours (depending on its type, humidity and temperature) is in the range of 100–300 MJ or 50 kWh, while the temperature inside the greenhouse is maintained at 50 –60 °С.

Flaws this method: effective thermal insulation of furnaces is impossible due to the risk of overheating and failure, for this reason these heating devices have low efficiency; In addition, the area of the defrosted area is small, and a powerful source of electricity is required to power the equipment; in addition, when the electrical contacts of the heating elements overheat, there is a high probability of electric shock to unauthorized persons; therefore, fencing and security of the area are required while the installation is operating. Due to these inconveniences and operational dangers, some companies refuse to use this heating method.

The arrangement of steam and water batteries is even more complicated; a steam or water boiler is required, etc.

Advantages . Fast and uncomplicated delivery to site and preparation for operation of equipment. Relatively short defrosting period – up to 10 hours.